While the need to protect human skin from solar radiation, particularly ultraviolet radiation, has been well documented during the past two decades, and a variety of preparations have been developed to provide varying degrees of "screening" or "blocking" therefrom, it has been found that the benefits of such compositions are readily lost when the user perspires or is engaged in water play which wahses off the protective coating thereby causing the benefits thereof to be quickly dissipated.
The need for a protective coating on the skin is essential because it is now proven that the sunlight contributes to aging and carcinogenesis by amplifying ultraviolet injury, altering the vasculature, producing diffusible mediators, changing histone binding properties, and/or damaging DNA repair processes. (See: Kaidbey, et al, Arch. Dermatol., 1982; 118 (5): 315-318.)
Ultraviolet and heat have been shown to synergistically denature human squamous buccal mucosal DNA. This work was carried out at 24.degree. C., 32.degree. C. (representing the temperature of indoor surface skin), and 42.degree. C. (representing the surface skin temperature in bright sunlight at 26.degree. North latitude). (See: Roth and London, J. Invest. Dermatol., 1977; 69; 368-372). Roth et al showed a positive linear relationship between DNA denaturation and irradiation temperature.
Principal considerations for selecting effective sunscreens include burning, tanning, and chronic changes such as, cancer, elastosis, wrinkling and pigmentary mottling. When considering the need for waterproofing protection, however, little information is available. Present sunscreens may protect against ultraviolet UVB and UVA. Unfortunately, they are usually non-substantive to skin and can easily be washed off by water or perspiration. As a result, many products on the market today will give consumers a false sense of security.
In an effort to address this problem, several compositions have been brought to market which contain a sunscreening agent and a water repellant in a cream or lotion base. However, in so far as they contribute certain desired properties, especially cosmetic properties to the skin, these compositions are not very elegant. They usually do not feel or appear like the conventional cosmetic creams or lotions made for other purposes and are usually very sticky, leaving an uncomfortable feel for the user. This tacky feel is usually caused by the polymer disposed in the sunscreen product in an attempt to effect water repellency. Therefore the conventional attempts had been the use of these plasticizers in cream/lotion bases with no work in the formulation of the cream/lotion base itself.
Moreover, the use of such polymers has additional drawbacks including "powdering" from too great a friability which further contributes to poor substantivity. Both cationic and anionic polymers can create this problem.
Accordingly, a real need exists in the industry for a waterproof composition especially useful with a sunscreen to provide effective protection for human skin from solar radiation with a magnitude of substantive integrity heretofore unavailable when anionic and cationic polymers are used to effect water repellency. It is toward this objective that the present invention is directed.